Hermetic seal



June 10, 1941- v. J. FRANCISrrAL HERMETIC SEAL Filed Jan. 27, 1941 Invenkors: Vickm- James Francis,

Eric KeflLeweLL b9 Their AHorne Patented June 10, 1941 Victor J. Francis, North Wembley, and Eric Kettlewell, Wembley Park. England, alsignors to General Electric New York Company, acorporation of Application January 21, 1941, Serial No. 378,228

I In Great Britain January 2, 1940 2 Claims. (01. 176-426) This invention relates to high pressure vapor electric discharge devices with envelopes of quartz or like material of the type in which at least one leading-in electrical conductor is introduced into the envelope by meansof an hermetic strip seal and in which, during full operation, the pressure exceeds'5 atm. Material like quartz means any vitreous, highly siliceous material having a coeilflcient of expansion not greater than 1.." per C. measured under conditions such that the coeillcient of expansion of quartz is 0.55x 10- per C. -In what follows. the word quartz will be used for brevity to mean quartz or like materia In the making of a strip seal, a quartz tube is usually collapsed onto both the strip itself and a stouter conductor to which the end of the strip is attached. Since the quartz shrinks away from the stouter conductor when the seal cools, an annulus is left between the quartz and the conductor terminated by a sharp angle. Again when,

as is usual, the device is made by sealing an I already prepared. strip seal into an aperture in the quartz envelope, an annulus is apt to be left between the quartzof the seal and the quartz of the envelope also terminated by a sharp angle. We have found 'thatthe presence of these sharp angles leads to mechanical weakness of the envelope which is apt to burst when a high vapor pressure is developed within it during operation of the device. The object of the invention is to avoid this diillculty and to increase the mechanical strength of such envelopes.

No method is known by which the presence of the sharp angle between the stout conductor and the quartz can be avoided. But we have discovered that the weakness of the envelope due to it can be greatly reduced by causing the gap terminating in the sharp angle to lie within the envelope, so that the pressure within the gap is opposed by pressure outside it.

The invention will be readily understood by an inspection of the accompanying drawing and a perusal of the following detailed description charge device of the high pressure embodying the improvement. Like numbers denote like parts in all the figures.

In the manufacture of the device a quartz tube is collapsed onto an electrical conductor comprising a thin, foil-like'strip ill of molybdenum, for example, to which a stouter conductor I is fastened as by welding. The conductor l consists of a wire or strip of refractory metal, such as molybdenum or tungsten, and is of such thickness that the quartz does not make an hermetic joint therewith as it does with the strip Ill. The

seal element or plug thus formed has a gap 5 between the stout conductor 4 and the quartz element I. The gap 5 is of appreciable depth and terminates in a sharp angle as shown in Fig. l of the drawing.

In prior structures the seal element has been fused into the tubular extension 2 of the envelope 3 of the discharge device as shown in Fig. 1

of the'dra wing, that is with the part of the quartz I surrounding the gap 5 outside the envelope 3 and in the extension 2. The pressure of the gaseous atmosphere in the envelope 3 is usually less than atmospheric pressure when the envelope 3 is, at room temperature and is 5 atmospheres and higher when the device is operating. During operation of the device the high pressure exerts force of considerable magnitude in the gap 5 tending to burst the seal as'indicated by the arrows inFig. 1. Since the gap terminates in a sharp angle, as pointed out above, it is a point of mechanical weakness of the device. In accordance with the present invention the part of the quartz element l surrounding the gap 5 is mounted within the space defined by the envelope 3 where the force tending to burst the seal is opposed by force tending to compress it, as indicated by the arrows in 3.

The sharp angle between the quartz element l and the envelope 3 characteristic of prior devices is shown at I in Fig. 1 of the drawing. This sharp angle is a weak part of the envelope 3 of the device which is strengthened by moving the quartz element I further into the envelope part 3 after these parts have been Joined by fusion and while the quartz is still plastic. The

' sharp angle I is thus changed to the much more gradual transition part l, as shown in Fig. 3, to

' increase the mechanical strength of the enve- 2 utilized to support the element i, which acts as a plugfor the envelope 8, in proper position in the tube 2 prior to the fusion of these elements,

' when desired. Fig. 2 shows the preferred position of the bulge 0' on the element I with respect to the angular opening about the conductor 4. The completed seal is shown in Fig. 8.

4 illustrates a complete discharge lamp having seals embodying the present invention.

Electrodes II are mounted on conductors l and are separated a few millimeters from each: other in the substantially spherical envelope 3. The envelope ,3 has therein a starting gas, such as neon; at a pressure of about 5 mm. and a quantity.12 of vaporizable material, such as mercury,

sufllcient to produce a vapor pressureofat least about 5 atmospheres during the operation of the lamp. The electrodes II are hollow, pointed, perforated metal shells, such as tungsten shells, con-- taining material of high electron emissivity characteristics, such as barium or strontium, or mixtures of such materials. As shown in Fig. 4 of the drawing the hermetic fused joint between the quartzelement I of the plug and the metal strip Iii terminates in the-space defined by the envelope 3 and the gap between the quartz element I and the conductor 4 is within said space.

The lamp described above is a long-lived compact,

mechanically strong, highly eillcient. light source of high intrinsic brilliancy.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An envelope for an. electric discharge device of the high pressure type, said envelope having a perforated part consisting of a vitreous material misses which the characteristics of quartz, a plug of similar vitreous material fused into and hermetically sealing said envelope part, said plug extending from the interior to theexterior of said err-f velope, and an electrical conductor extending through said plug, saidconductor comprising a thin, foil-like strip of metal hermetically fused into and terminating in said plug at an apprecia.

ble distance from the end of said plug in said envelope and a metal wire connected to said strip lope comprising a cylindricalmember of quartz,

an electrical conductor sealed through said cylindrical member, said conductor comprising a thin. foil-like strip of metal hermetically fused into and terminating within said cylindrical member and a metal body connected to said strip in said cylindrical member and extending beyond said cylindrical member, said metal bodybeing incapable of making a hermetic Joint with said cylin cal member, said cylindrical member having an annular protuberance thereon between the ends of said metal strip for supporting said seal in said envelope and providing material for the formation of a rounded surface between said envelope and said cylindrical member when these eiements are combined by fusion; i

VICTOR J. FRANCIS. ERIC KE'I'ILEIWELL. 

